Solid-state image sensor, imaging device, and method of controlling solid-state image sensor

ABSTRACT

In a solid-state image sensor that transfers electric charges to a floating diffusion layer, exposure is started before transferring the electric charges to the floating diffusion layer. Electric charges are generated by photoelectric conversion in a photodiode and they are accumulated in an accumulation unit. An exposure end transfer transistor transfers the electric charges from the photodiode to the accumulation unit when a predetermined exposure period ends. A reset transistor initializes a voltage of a floating diffusion layer to a predetermined reset level when the exposure period ends. When a new exposure period is started after the electric charges are transferred to the accumulation unit, a discharge transistor discharges electric charges newly generated in the photodiode. When processing of converting a predetermined reset level into a digital signal ends, a conversion end transistor transfers the electric charges from the accumulation unit to the floating diffusion layer.

TECHNICAL FIELD

The present technology relates to a solid-state image sensor, an imagingdevice, and a method of controlling a solid-state image sensor.Specifically, the present technology relates to a solid-state imagesensor that accumulates electric charges in a floating diffusion layer,an imaging device, and a method of controlling a solid-state imagesensor.

BACKGROUND ART

Conventionally, in a solid-state image sensor, a global shutter systemhas been used in which the start and end of exposure can be aligned forall pixels. For example, a solid-state image sensor that enables aglobal shutter system by providing an analog to digital (AD) converterin all pixels has been proposed (see Patent Document 1, for example). Inthis solid-state image sensor, a photodiode, a transfer transistor, areset transistor, a discharge transistor, and the like are provided inthe pixel in addition to the AD converter. The discharge transistorinitializes the photodiode at the start of exposure, and the resettransistor initializes a floating diffusion layer immediately before theend of exposure. Then, at the end of exposure, the transfer transistortransfers electric charges from the photodiode to the floating diffusionlayer. Additionally, the AD converter AD-converts the reset level at thetime of initialization of the floating diffusion layer and the signallevel at the time of transfer.

CITATION LIST PATENT DOCUMENT

Patent Document 1: International Patent Application Publication No.2016/136448

SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

The solid-state image sensor described above can capture image datawithout rolling shutter distortion by adopting the global shuttersystem. However, in the above-mentioned solid-state image sensor, thereis a problem that the exposure cannot be started from immediately afterthe initialization of the floating diffusion layer to immediately beforethe transfer of electric charges, that is, within the period of ADconversion of the reset level. This is because if the photodiode isinitialized before the electric charges corresponding to the exposureamount in the photodiode are transferred to the floating diffusionlayer, the electric charges before AD conversion disappear and the imagedata is destroyed.

The present technology has been made in view of such a situation, and anobject of the present technology is to, in a solid-state image sensorthat transfers electric charges to a floating diffusion layer, startexposure before transferring the electric charges to the floatingdiffusion layer.

SOLUTIONS TO PROBLEMS

The present technology has been made in order to solve the aboveproblems, and a first aspect thereof is a solid-state image sensorincluding: a photodiode that generates electric charges by photoelectricconversion; an electric charge accumulation unit that accumulates theelectric charges; a floating diffusion layer that converts the electriccharges into a signal level corresponding to the amount of the electriccharges; an exposure end transfer transistor that transfers the electriccharges from the photodiode to the electric charge accumulation unitwhen a predetermined exposure period ends; a reset transistor thatinitializes a voltage of the floating diffusion layer to a predeterminedreset level when the exposure period ends; a discharge transistor that,when a new exposure period is started after the electric charges aretransferred to the electric charge accumulation unit, dischargeselectric charges newly generated in the photodiode; and a conversion endtransfer transistor that, when processing of converting a predeterminedreset level into a digital signal ends, transfers the electric chargesfrom the electric charge accumulation unit to the floating diffusionlayer, and a method of controlling the solid-state image sensor. Thisbrings about an effect that electric charges are transferred from thephotodiode to the electric charge accumulation unit before the electriccharges are transferred to the floating diffusion layer.

Additionally, in the first aspect, the solid-state image sensor mayfurther include an analog-to-digital converter that sequentiallyperforms reset level conversion processing of converting the reset levelinto the digital signal, and signal level conversion processing ofsequentially converting the signal level into a digital signal. Thisbrings about the effect that the reset level and the signal level aresequentially converted into digital signals.

Additionally, in the first aspect, the photodiode, the electric chargeaccumulation unit, the floating diffusion layer, the exposure endtransfer transistor, the discharge reset transistor, the conversion endtransfer transistor, and the reset transistor may be arranged on apredetermined light receiving board, and at least a part of theanalog-to-digital converter may be arranged on a predetermined circuitboard stacked on the predetermined light receiving board. This bringsabout an effect that electric charges are transferred in the solid-stateimage sensor having a stacked structure.

Additionally, in the first aspect, the solid-state image sensor mayfurther include a source follower transistor that has a gate connectedto the floating diffusion layer and a drain connected to a power supplyterminal, a selection transistor that outputs a signal from a source ofthe source follower transistor to the analog-to-digital converteraccording to a predetermined selection signal, and a cascode transistorthat is cascode-connected to the selection transistor. This brings aboutan effect that the pixel signal of a selected pixel is read out.

Additionally, in the first aspect, the photodiode, the electric chargeaccumulation unit, the floating diffusion layer, the exposure endtransfer transistor, the photodiode reset transistor, the conversion endtransfer transistor, and the floating diffusion layer reset transistormay be arranged in each of multiple pixels. This brings about an effectthat electric charges are transferred for each pixel.

Additionally, in the first aspect, the electric charge accumulationunit, the exposure end transfer transistor, and the conversion endtransfer transistor may be arranged in each of multiple memory circuitssharing the photodiode and the floating diffusion layer. This bringsabout an effect that electric charges are transferred to any of multiplememory circuits.

Additionally, in the first aspect, the analog-to-digital converter maybe arranged in each of the multiple pixels. As a result, exposure can bestarted simultaneously for all pixels.

Additionally, in the first aspect, the analog-to-digital converter maybe arranged in each of multiple pixel blocks each including apredetermined number of pixels. This brings about an effect thatexposure is started for any pixel in each pixel block.

Additionally, in the first aspect, the analog-to-digital converter mayrepeat the reset level conversion processing from the beginning in acase where the amount of the electric charges in the photodiode isinitialized during the reset level conversion processing. This bringsabout an effect that offset is removed.

Additionally, in the first aspect, the analog-to-digital converter mayrepeat the signal level conversion processing from the beginning in acase where the amount of the electric charges in the photodiode isinitialized during the signal level conversion processing. This bringsabout an effect that offset is removed.

Additionally, in the first aspect, the solid-state image sensor mayfurther include a signal processing unit that performs correlated doublesampling processing for obtaining, as image data, a difference betweenthe digital signal obtained by converting the reset level and thedigital signal obtained by converting the signal level. This bringsabout an effect that fixed pattern noise is removed.

Additionally, in the first aspect, the signal processing unit mayfurther perform dark current correction for removing dark current fromthe image data. This brings about an effect that offset is removed.

Additionally, a second aspect of the present technology is an imagingdevice including: a photodiode that generates electric charges byphotoelectric conversion; an electric charge accumulation unit thataccumulates the electric charges; a floating diffusion layer thatconverts the electric charges into a signal level corresponding to theamount of the electric charges; an exposure end transfer transistor thattransfers the electric charges from the photodiode to the electriccharge accumulation unit when a predetermined exposure period ends; areset transistor that initializes a voltage of the floating diffusionlayer to a predetermined reset level when the exposure period ends; adischarge transistor that, when a new exposure period is started afterthe electric charges are transferred to the electric charge accumulationunit, discharges electric charges newly generated in the photodiode; aconversion end transfer transistor that, when processing of converting apredetermined reset level into a digital signal ends, transfers theelectric charges from the electric charge accumulation unit to thefloating diffusion layer; and a signal processing unit that processesthe digital signal obtained by converting the reset level and a digitalsignal obtained by converting the signal level. This brings about aneffect that electric charges are transferred from the photodiode to theelectric charge accumulation unit and the digital signals are processedbefore the electric charges are transferred to the floating diffusionlayer.

EFFECTS OF THE INVENTION

According to the present technology, in a solid-state image sensor thattransfers electric charges to a floating diffusion layer, an excellenteffect that exposure can be started before transferring electric chargesto the floating diffusion layer can be achieved. Note that the effectdescribed herein is not necessarily limited, and the effect may be anyof those described in the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for describing a usage example of an imaging deviceaccording to a first embodiment of the present technology.

FIG. 2 is a block diagram showing a configuration example of the imagingdevice of the first embodiment of the present technology.

FIG. 3 is a block diagram showing a configuration example of asolid-state image sensor of the first embodiment of the presenttechnology.

FIG. 4 is an example of a plan view of a pixel array unit of the firstembodiment of the present technology.

FIG. 5 is a block diagram showing a configuration example of a pixel ofthe first embodiment of the present technology.

FIG. 6 is a circuit diagram showing a configuration example of a pixelcircuit, a differential input circuit, a voltage conversion circuit, anda positive feedback circuit of the first embodiment of the presenttechnology.

FIG. 7 is a diagram showing an example of a layout of elements in thepixel circuit of the first embodiment of the present technology.

FIG. 8 is a timing chart showing an example of the operation of theimaging device of the first embodiment of the present technology.

FIG. 9 is an example of a timing chart in a case where no trigger signalis input during AD conversion in the first embodiment of the presenttechnology.

FIG. 10 is an example of a timing chart in a case where a trigger signalis input during conversion of a reset level in the first embodiment ofthe present technology.

FIG. 11 is an example of a timing chart in a case where a trigger signalis input during transfer of electric charges in the first embodiment ofthe present technology.

FIG. 12 is an example of a timing chart in a case where a trigger signalis input during signal level conversion in the first embodiment of thepresent technology.

FIG. 13 is an example of a state transition diagram showing theoperation of the solid-state image sensor of the first embodiment of thepresent technology.

FIG. 14 is a flowchart showing an example of the operation of theimaging device of the first embodiment of the present technology.

FIG. 15 is a circuit diagram showing a configuration example of a pixelcircuit, a differential input circuit, a voltage conversion circuit, anda positive feedback circuit of a first modification of the firstembodiment of the present technology.

FIG. 16 is an example of a state transition diagram of a secondmodification of the first embodiment of the present technology.

FIG. 17 is a timing chart of the second modification of the firstembodiment of the present technology.

FIG. 18 is an example of a plan view of a pixel array unit of a thirdmodification of the first embodiment of the present technology.

FIG. 19 is an example of a state transition diagram of the thirdmodification of the first embodiment of the present technology.

FIG. 20 is a timing chart of the third modification of the firstembodiment of the present technology.

FIG. 21 is an example of a plan view of a pixel array unit of a secondembodiment of the present technology.

FIG. 22 is a block diagram showing a configuration example of a pixelblock of the second embodiment of the present technology.

FIG. 23 is a timing chart showing an example of the operation of animaging device of the second embodiment of the present technology.

FIG. 24 is a circuit diagram showing a configuration example of a pixelcircuit of a third embodiment of the present technology.

FIG. 25 is a block diagram showing a schematic configuration example ofa vehicle control system.

FIG. 26 is an explanatory diagram showing an example of an installationposition of an imaging unit.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, modes for carrying out the present technology (hereinafterreferred to as embodiments) will be described. The description will begiven in the following order.

1. First embodiment (example in which electric charges are transferredfrom photodiode to analog memory)

2. Second embodiment (example in which electric charges are transferredfrom photodiode to analog memory in pixel of shared structure)

3. Third embodiment (example in which electric charges are transferredfrom photodiode to one of multiple analog memories)

4. Example of application to movable body

1. First Embodiment

FIG. 1 is a diagram for describing a usage example of an imaging device100 according to a first embodiment of the present technology. Theimaging device 100 is used in a line inspection of factory automation,for example. In the line inspection, when a product 511 conveyed at highspeed by a belt conveyor 510 reaches a predetermined position on amanufacturing line, a detection sensor 520 detects this state. As thedetection sensor 520, an infrared sensor is used, for example.

Upon detection, the detection sensor 520 transmits a trigger signalXTRIG giving an instruction on the start of imaging to the imagingdevice 100, and the imaging device 100 images the product 511 andgenerates image data. Note, however, that the imaging device 100 cannotstart the next exposure for a certain period immediately after theelapse of an exposure period in imaging. Such a period in which the nextexposure cannot be started even if the trigger signal XTRIG is input ishereinafter referred to as a “dead period”. Then, by analyzing the imagedata, the manufacturing system can inspect whether or not there is anabnormality in the product 511, for example.

Here, in a case where the product 511 is not necessarily conveyed by thebelt conveyor 510 at regular intervals, the trigger signal XTRIG isgenerated randomly. Such a trigger signal is called a random trigger. Inthe case of performing imaging according to random triggers, a shorterdead period is more preferable from the viewpoint of performing lineinspection at high speed.

Note that while the imaging device 100 is used for factory automation,the present invention is not limited to this example as long as imagingis performed at random timings. For example, in a crime preventionsystem, the imaging device 100 may start imaging when an infrared sensordetects a suspicious person or the like.

[Configuration Example of Imaging Device]

FIG. 2 is a block diagram showing a configuration example of the imagingdevice 100 of the first embodiment of the present technology. Theimaging device 100 is a device for capturing image data, and includes anoptical unit 110, a solid-state image sensor 200, and a digital signalprocessing (DSP) circuit 120. Moreover, the imaging device 100 includesa display unit 130, an operation unit 140, a bus 150, a frame memory160, a storage unit 170, and a power supply unit 180.

The optical unit 110 collects light from a subject and guides it to thesolid-state image sensor 200. The solid-state image sensor 200 capturesimage data when the trigger signal XTRIG is input. The solid-state imagesensor 200 supplies the captured image data to the DSP circuit 120through a signal line 209.

The DSP circuit 120 performs predetermined signal processing on theimage data from the solid-state image sensor 200. The DSP circuit 120outputs the processed image data to the frame memory 160 or the likethrough the bus 150.

The display unit 130 displays image data. As the display unit 130 aliquid crystal panel or an organic electro luminescence (EL) panel maybe used, for example. The operation unit 140 generates an operationsignal according to a user operation.

The bus 150 is a common path for the optical unit 110, the solid-stateimage sensor 200, the DSP circuit 120, the display unit 130, theoperation unit 140, the frame memory 160, the storage unit 170, and thepower supply unit 180 to exchange data with each other.

The frame memory 160 holds image data. The storage unit 170 storesvarious data such as image data. The power supply unit 180 suppliespower to the solid-state image sensor 200, the DSP circuit 120, thedisplay unit 130, and the like.

[Configuration Example of Solid-State Image Sensor]

FIG. 3 is a block diagram showing a configuration example of thesolid-state image sensor 200 of the first embodiment of the presenttechnology. The solid-state image sensor 200 includes a digital toanalog converter (DAC) 210 and multiple time code generation units 220.Additionally, the solid-state image sensor 200 also includes a verticaldriving circuit 230, a pixel array unit 240, a pixel driving circuit250, a timing generation circuit 260, and a signal processing unit 270.Additionally, in the pixel array unit 240, multiple pixels are arrangedin a two-dimensional lattice shape.

The DAC 210 generates an analog reference signal that changes in a slopeshape by digital to analog (DA) conversion. The DAC 210 supplies thereference signal to the pixel array unit 240.

The time code generation unit 220 generates a time code. The time codeindicates the time within a period when the reference signal changes ina slope shape. The time code generation unit 220 supplies the generatedtime code to the pixel array unit 240.

The timing generation circuit 260 generates various timing signals whenthe trigger signal XTRIG is input and supplies the timing signals to thevertical driving circuit 230, the pixel driving circuit 250, the signalprocessing unit 270, and the like.

The vertical driving circuit 230 performs control to output pixel datagenerated in a pixel to the signal processing unit 270 insynchronization with a timing signal. The pixel driving circuit 250drives pixels.

The signal processing unit 270 performs signal processing includingcorrelated double sampling (CDS) processing on pixel data. The CDSprocessing removes fixed pattern noise from image data. The signalprocessing unit 270 outputs the processed pixel data to the DSP circuit120. Note that a part or all of the processing in the signal processingunit 270 can be performed by a circuit (DSP circuit 120 or the like)outside the solid-state image sensor 200.

[Configuration Example of Pixel Array Unit]

FIG. 4 is a block diagram showing a configuration example of the pixelarray unit 240 of the first embodiment of the present technology. Thepixel array unit 240 includes multiple time code transfer sections 241and multiple pixels 300. The time code transfer section 241 is arrangedfor each time code generation unit 220. Additionally, the pixels 300 arearranged in a two-dimensional lattice shape.

The time code transfer section 241 transfers the time code from thecorresponding time code generation unit 220. The time code transfersection 241 transfers the time code from the corresponding time codegeneration unit 220 to the pixel 300, and transfers the time code fromthe pixel 300 to the signal processing unit 270 as pixel data. The pixel300 generates pixel data.

<Configuration Example of Pixel>

FIG. 5 is a block diagram showing a configuration example of the pixel300 of the first embodiment of the present technology. The pixel 300includes a pixel circuit 310 and an ADC 320. The ADC 320 includes acomparator circuit 321 and a data storage section 360. Additionally, thecomparator circuit 321 includes a differential input circuit 330, avoltage conversion circuit 340, and a positive feedback circuit 350.

The pixel circuit 310 generates a reset level or a signal level as apixel signal SIG by photoelectric conversion. Here, the reset level is avoltage when the floating diffusion layer is initialized, and the signallevel is a voltage when electric charges are transferred to the floatingdiffusion layer. The circuit configuration of the pixel circuit 310including the floating diffusion layer will be described later. Thepixel circuit 310 sequentially supplies the reset level and the signallevel to the differential input circuit 330. The reset level willhereinafter be referred to as “P-phase level”. Additionally, the signallevel will hereinafter be referred to as “D-phase level”.

The ADC 320 AD-converts the pixel signal SIG (P-phase level or D-phaselevel) into a digital signal. The digital signal obtained byAD-converting the P-phase level will hereinafter be referred to as“P-phase data”. Additionally, the digital signal obtained byAD-converting the D-phase level will hereinafter be referred to as“D-phase data”.

The differential input circuit 330 in the ADC 320 compares a referencesignal REF from the DAC 210 with the pixel signal SIG from the pixelcircuit 310. The differential input circuit 330 supplies a comparisonresult signal indicating the comparison result to the voltage conversioncircuit 340.

The voltage conversion circuit 340 converts the voltage of thecomparison result signal from the differential input circuit 330 andoutputs it to the positive feedback circuit 350.

The positive feedback circuit 350 adds a part of its output to the input(comparison result signal), and outputs it as an output signal VCO tothe data storage section 360.

The data storage section 360 holds the time code when the output signalVCO is inverted. The data storage section 360 outputs the time codecorresponding to the P-phase level as P-phase data and the time codecorresponding to the D-phase level as D-phase data.

FIG. 6 is a circuit diagram showing a configuration example of the pixelcircuit 310, the differential input circuit 330, the voltage conversioncircuit 340, and the positive feedback circuit 350 of the firstembodiment of the present technology.

The pixel circuit 310 includes a reset transistor 311, a floatingdiffusion layer 312, a transfer transistor 313, an analog memory 314, atransfer transistor 315, a photodiode 316, and a discharge transistor317. N-type metal-oxide-semiconductor (MOS) transistors are used as thereset transistor 311, the transfer transistor 313, the transfertransistor 315, the photodiode 316, and the discharge transistor 317,for example.

The photodiode 316 generates electric charges by photoelectricconversion. The discharge transistor 317 discharges electric chargesaccumulated in the photodiode 316 according to a drive signal OFG fromthe pixel driving circuit 250. The discharging of electric chargesinitializes the photodiode 316.

The transfer transistor 315 transfers electric charges from thephotodiode 316 to the analog memory 314 according to a transfer signalTRX from the pixel driving circuit 250. The transfer signal TRX issupplied at the end of an exposure period. Note that the transfertransistor 315 is an example of an exposure end transfer transistordescribed in the claims.

The analog memory 314 stores electric charges. While the analog memory314 can be formed by the wiring capacitance in principle, it isdesirable to use a buried-type capacitance capable of full depletion toenable transfer of electric charges to the floating diffusion layer 312.Note that the analog memory 314 is an example of an electric chargeaccumulation unit described in the claims.

The transfer transistor 313 transfers electric charges from the analogmemory 314 to the floating diffusion layer 312 according to a transfersignal TRG from the pixel driving circuit 250. The transfer signal TRGis supplied when AD conversion of the P-phase level (reset level) iscompleted. Note that the transfer transistor 313 is an example of aconversion end transfer transistor described in the claims.

The floating diffusion layer 312 accumulates the transferred electriccharges and generates a voltage according to the amount of the electriccharges.

The reset transistor 311 initializes the voltage of the floatingdiffusion layer 312 to a reset level according to a reset signal RSTfrom the pixel driving circuit 250. The reset signal RST is supplied atthe end of an exposure period.

The differential input circuit 330 includes positive channel MOS (PMOS)transistors 331, 334, and 336 and negative channel MOS (NMOS)transistors 332, 333, and 335.

The NMOS transistors 332 and 335 form a differential pair, and thesources of these transistors are commonly connected to the drain of theNMOS transistor 333. Additionally, the drain of the NMOS transistor 332is connected to the drain of the PMOS transistor 331 and the gates ofthe PMOS transistors 331 and 334. The drain of the NMOS transistor 335is connected to the drain of the PMOS transistor 334, the gate of thePMOS transistor 336, and the drain of the reset transistor 311.Additionally, the reference signal REF is input to the gate of the NMOStransistor 332.

A predetermined bias voltage Vb is applied to the gate of the NMOStransistor 333, and a predetermined ground voltage is applied to thesource of the NMOS transistor 333.

The PMOS transistors 331 and 334 form a current mirror circuit. A powersupply voltage VDDH is applied to the sources of the PMOS transistors331, 334, and 336. The power supply voltage VDDH is higher than a powersupply voltage VDDL. Additionally, the drain of the PMOS transistor 336is connected to the voltage conversion circuit 340.

The voltage conversion circuit 340 includes an NMOS transistor 341. Thepower supply voltage VDDL is applied to the gate of the NMOS transistor341. Additionally, the drain of the NMOS transistor 341 is connected tothe drain of the PMOS transistor 336, and the source of the NMOStransistor 341 is connected to the positive feedback circuit 350.

The positive feedback circuit 350 includes PMOS transistors 351, 352,355, and 356 and NMOS transistors 353, 354, and 357. The PMOStransistors 351 and 352 are connected in series with the power supplyvoltage VDDL. Moreover, a drive signal INI2 from the vertical drivingcircuit 230 is input to the gate of the PMOS transistor 351. The drainof the PMOS transistor 352 is connected to the source of the NMOStransistor 341, the drain of the NMOS transistor 353, and the gates ofthe PMOS transistor 355 and the NMOS transistor 354.

The ground voltage is applied to the source of the NMOS transistor 353,and a drive signal INI1 from the vertical driving circuit 230 is inputto the gate of the NMOS transistor 353.

The PMOS transistors 355 and 356 are connected in series with the powersupply voltage VDDL. Additionally, the drain of the PMOS transistor 356is connected to the gate of the PMOS transistor 352 and the drains ofthe NMOS transistors 354 and 357. A control signal TESTVCO from thevertical driving circuit 230 is input to the gates of the PMOStransistor 356 and the NMOS transistor 357.

The output signal VCO is output from the drains of the NMOS transistors354 and 357. Additionally, the ground voltage is applied to the sourcesof the NMOS transistors 354 and 357.

Additionally, the NMOS transistors 332, 333, and 335 and the pixelcircuit 310 are arranged on a light receiving chip 201. The PMOStransistors 331, 334, and 336 and the voltage conversion circuit 340 andfollowing circuits are arranged on a circuit chip 202 stacked on thelight receiving chip 201. These chips are electrically connected througha connection part such as a via. Note that other than vias, Cu-Cubonding or bumps can be used for connection.

Note that while the light receiving chip 201 and the circuit chip 202are separated in the differential input circuit 330, the separating partis not limited to this configuration. For example, the light receivingchip 201 and the circuit chip 202 can be separated at a connection pointbetween the pixel circuit 310 and the differential input circuit 330.Additionally, while the circuits in the solid-state image sensor 200have a stacked structure in which the circuits are dispersedly arrangedon the light receiving chip 201 and the circuit chip 202 stacked on topof one another, the circuits may be arranged on one chip. Additionally,each of the differential input circuit 330, the voltage conversioncircuit 340, and the positive feedback circuit 350 is not limited to thecircuit illustrated in FIG. 6 as long as it has the function describedin FIG. 5.

Here, a comparative example is assumed in which the analog memory 314and the transfer transistor 315 are not provided, and the transfertransistor 313 transfers electric charges from the photodiode 316 to thefloating diffusion layer 312. In the comparative example, exposurecannot be started during AD conversion (within so-called readingperiod). Before transfer of electric charges, that is, during theconversion of the P-phase level (reset level), electric chargescorresponding to the exposure amount are still accumulated in thephotodiode 316. Hence, if exposure is started at this time, thephotodiode 316 will be initialized and image data will be destroyed.Additionally, if exposure is started during AD conversion of the D-phaselevel (signal level), analog fluctuation due to initialization of thephotodiode 316 will adversely affect the AD conversion result. Since theADC 320 is arranged in all the pixels, evenly offsetting the in-planewill result in different values in the frame. In order to prevent imagedata destruction and offset fluctuation, it is necessary to ignore thetrigger signal XTRIG during AD conversion or start exposure after ADconversion is completed.

On the other hand, unlike the comparative example, the pixel circuit 310further includes the analog memory 314 and the transfer transistor 315,and the transfer transistor 315 transfers electric charges to the analogmemory 314 at the end of exposure. For this reason, even if the exposureis started (i.e., photodiode 316 is initialized) during AD conversion ofthe P-phase level, the electric charges in the analog memory 314 do notdisappear. Additionally, offset fluctuation due to initialization of thephotodiode 316 can be reduced by redoing of the AD conversion, whichwill be described later. Hence, the solid-state image sensor 200 canstart exposure during AD conversion, and the dead period can be madeshorter than in the comparative example.

With the configuration in which the analog memory 314 and the transfertransistor 315 are added, in a case where the AD conversion period islonger than the exposure period, the dead period is represented by thefollowing formula.

(Dead period)=(transfer period)+(AD conversion period−exposure period)

In the above formula, “transfer period” is a period during which thetransfer transistor 315 transfers the electric charges from thephotodiode 316 to the analog memory 314.

On the other hand, in a case where the length of the AD conversionperiod is equal to or shorter than the exposure period, the transferperiod is equal to the dead period. Accordingly, the dead period can bemade even shorter by shortening the AD conversion period or the transferperiod.

Note that the configuration of the ADC 320 is not limited to theconfiguration illustrated in FIGS. 5 and 6 as long as it can perform ADconversion. For example, a reset switch of the comparator circuit 321for auto-zero drive or a DC blocking capacitor may be added.

FIG. 7 is a diagram showing an example of a layout of elements in thepixel circuit 310 according to the first embodiment of the presenttechnology. The analog memory 314 is arranged adjacent to the photodiode316, and the transfer transistor 315 is arranged at a positionoverlapping with the photodiode 316 and the analog memory 314.Additionally, the discharge transistor 317 is arranged at the dischargedestination of the photodiode 316, and the transfer transistor 313 isarranged at the transfer destination of the analog memory 314.

Additionally, the NMOS transistor 333, the reset transistor 311, and theNMOS transistors 335 and 332 are arranged in a predetermined direction.

[Operation Example of Imaging Device]

FIG. 8 is a flowchart showing an example of the operation of the imagingdevice 100 of the first embodiment of the present technology. Thedetection sensor 520 generates the trigger signal XTRIG at randomtimings such as timings T1, T3, and T7, and inputs the trigger signalXTRIG to the imaging device 100.

On the other hand, in the pixel circuit 310 in the imaging device 100,all pixels are simultaneously exposed for a certain exposure period fromtimings T1, T3, and T7 of the trigger signal XTRIG. That is, the globalshutter system is used. Additionally, at timings T2 and T6 when theexposure ends, the ADCs 320 of all the pixels sequentially convert theP-phase level and the D-phase level. For example, the ADC 320 convertsthe P-phase level during the period from timing T2 to T4 and convertsthe D-phase level during the period from timing T4 to T5. Note that,strictly speaking, there are a period required for initializing thephotodiode 316 and the floating diffusion layer 312 and a transferperiod required for transfer of electric charges. However, these periodsare extremely short, and are therefore omitted in FIG. 8.

As described above, the electric charges of the photodiode 316 aretransferred to the analog memory 314 at timing T2 when the exposureperiod ends. For this reason, at timing T3 during the conversion of theP-phase level from timing T2 to T4, even if the trigger signal XTRIG isinput, the pixel circuit 310 can start the next new exposure period(i.e., can initialize photodiode 316).

As described above, in the solid-state image sensor 200, the pixelcircuit 310 can concurrently start the next new exposure while the ADC320 is performing AD conversion. In other words, the solid-state imagesensor 200 can operate the ADC 320 and the pixel circuit 310 in paralleland perform pipeline driving.

Note that in a case where the trigger signal XTRIG is input during anexposure period, the solid-state image sensor 200 cannot start the nextexposure because the electric charges in the photodiode 316 have notbeen transferred. In this case, the solid-state image sensor 200 waitsuntil the exposure end timing before starting the next exposure, forexample.

FIG. 9 is an example of a timing chart in a case where no trigger signalis input during AD conversion in the first embodiment of the presenttechnology. When the trigger signal XTRIG is input at timing T1, thepixel driving circuit 250 supplies the high-level drive signal OFG untiltiming T11 when a predetermined pulse period elapses. As a result, thephotodiode 316 is initialized.

Then, from timing T11 to timing T12 when a certain exposure periodelapses, the photodiode 316 generates and accumulates electric chargesby photoelectric conversion. The pixel driving circuit 250 supplies thehigh-level transfer signal TRX for a pulse period from timing T12 whenthe exposure ends. As a result, electric charges are transferred fromthe photodiode 316 to the analog memory 314.

Additionally, at timing T13 immediately after timing T12, the pixeldriving circuit 250 supplies the high-level reset signal RST for a pulseperiod. As a result, the floating diffusion layer 312 is initialized.

Immediately after timing T14 when the initialization of the floatingdiffusion layer 312 ends, the vertical driving circuit 230 supplies thedrive signals INI1 and INI2 and sets the control signal TESTVCO to thelow level. The DAC 210 supplies a sawtooth reference signal REF. As aresult, the P-phase level is AD-converted.

From timing T15 when the AD conversion of the P-phase level ends totiming T16 when the pulse period elapses, the pixel driving circuit 250supplies the high-level transfer signal TRG. As a result, electriccharges are transferred from the analog memory 314 to the floatingdiffusion layer 312.

Then, immediately after timing T16, the vertical driving circuit 230supplies the drive signals INI1 and INI2 and sets the control signalTESTVCO to the low level. The DAC 210 supplies a sawtooth referencesignal REF. As a result, the D-phase level is AD-converted.

After timing T17 when the conversion of the D-phase level ends, thesignal processing unit 270 performs CDS processing for obtaining thedifference between the P-phase data and the D-phase data as net pixeldata.

FIG. 10 is an example of a timing chart in a case where a trigger signalis input during the conversion of the reset level in the firstembodiment of the present technology. The control up to timing T14 whenthe initialization of the floating diffusion layer 312 ends is similarto that in FIG. 9.

When the trigger signal XTRIG is input at timing T15 during ADconversion of the P-phase level (reset level), the pixel driving circuit250 supplies the high-level drive signal OFG until timing T16 when apredetermined pulse period elapses. As a result, the photodiode 316 isinitialized.

It is known that if the photodiode 316 is initialized during the ADperiod as described above, the parasitic capacitance unit such as thefloating node fluctuates, resulting in an incorrect AD conversion value.Against this background, in this case, the solid-state image sensor 200stops the slope output of the P-phase level reference signal REF andredoes the operation from the start of the P-phase acquisition sequence.

For example, immediately after timing T16, the vertical driving circuit230 supplies the drive signals INI1 and INI2 and sets the control signalTESTVCO to the low level. The DAC 210 supplies a sawtooth referencesignal REF. As a result, the P-phase level is AD-converted. Note that bygenerating a pulse so that the pair of the drive signals INI1 and INI2becomes high and low or low and high immediately after theinitialization of the floating diffusion layer 312, it is possible tocurb coupling of potentials of the analog signal and the floating node,for example.

FIG. 11 is an example of a timing chart in a case where a trigger signalis input during transfer of electric charges in the first embodiment ofthe present technology. The control up to timing T15 when the ADconversion of the P-phase level (reset level) ends is similar to that inFIG. 9. When the trigger signal XTRIG is input at timing T16 within thetransfer period to the floating diffusion layer 312, the pixel drivingcircuit 250 supplies the high-level drive signal OFG until the pulseperiod elapses. As a result, the photodiode 316 is initialized. Thecontrol at and after timing T17 when the transfer of electric charges tothe floating diffusion layer 312 ends is similar to that in FIG. 9.

Note that in a case where the trigger signal XTRIG is input duringinitialization of the floating diffusion layer 312, too, the photodiode316 is initialized as in the case where the trigger signal XTRIG isinput during transfer, and the AD conversion is not repeated.

FIG. 12 is an example of a timing chart in a case where a trigger signalis input during signal level conversion in the first embodiment of thepresent technology. The control up to timing T16 when the transfer ofelectric charges to the floating diffusion layer 312 ends is similar tothat in FIG. 9. When the trigger signal XTRIG is input at timing T17during AD conversion of the D-phase level (signal level), the pixeldriving circuit 250 supplies the high-level drive signal OFG untiltiming T18 when a predetermined pulse period elapses. As a result, thephotodiode 316 is initialized.

The solid-state image sensor 200 stops the slope output of the D-phaselevel reference signal REF and redoes the operation from the start ofthe D-phase acquisition sequence. For example, immediately after timingT18, the vertical driving circuit 230 supplies the drive signals INI1and INI2 and sets the control signal TESTVCO to the low level. The DAC210 supplies a sawtooth reference signal REF. As a result, the D-phaselevel is AD-converted.

FIG. 13 is an example of a state transition diagram showing theoperation of the solid-state image sensor 200 of the first embodiment ofthe present technology.

When the exposure is completed, the solid-state image sensor 200transfers the electric charges to the analog memory 314 and shifts to astate 620 where the floating diffusion layer 312 is initialized. Whenthe trigger signal XTRIG is input during the initialization of thefloating diffusion layer 312, the solid-state image sensor 200 shifts toa state 600 where the photodiode 316 is initialized (i.e., exposure isstarted) in parallel with the initialization of the floating diffusionlayer 312.

When the initialization of the floating diffusion layer 312 iscompleted, the solid-state image sensor 200 shifts to a state 650 wherethe P-phase level (reset level) is AD-converted. When the trigger signalXTRIG is input during P-phase conversion, the solid-state image sensor200 shifts to a state 630 where the photodiode 316 is initialized. Whenthe initialization is completed, the solid-state image sensor 200returns to the state 650 and repeats the P-phase conversion from thebeginning.

Then, when the P-phase conversion is completed, the solid-state imagesensor 200 shifts to a state 660 where electric charges are transferredto the floating diffusion layer 312. When the trigger signal XTRIG isinput during the transfer to the floating diffusion layer 312, thesolid-state image sensor 200 shifts to a state 670 where the photodiode316 is initialized in parallel with the transfer of electric charges.

When the transfer to the floating diffusion layer 312 is completed, thesolid-state image sensor 200 shifts to a state 640 where the D-phaselevel (signal level) is AD-converted. When the trigger signal XTRIG isinput during D-phase conversion, the solid-state image sensor 200 shiftsto a state 610 where the photodiode 316 is initialized. When theinitialization is completed, the solid-state image sensor 200 returns tothe state 640 and repeats the D-phase conversion from the beginning.When the D-phase conversion is completed, the solid-state image sensor200 shifts to the state 620 after the exposure is completed.

FIG. 14 is a flowchart showing an example of the operation of theimaging device 100 of the first embodiment of the present technology.This operation is started when the trigger signal XTRIG is input, forexample.

First, the solid-state image sensor 200 initializes the photodiode 316and starts exposure (step S901). Then, the solid-state image sensor 200determines whether or not the exposure period has ended (step S902). Ifthe exposure period has not ended (step S902: No), the solid-state imagesensor 200 repeats step S902.

If the exposure period has ended (step S902: Yes), the solid-state imagesensor 200 transfers electric charges to the analog memory 314 (stepS903) and initializes the floating diffusion layer 312 (step S904). Notethat when the trigger signal XTRIG is input during the initialization ofthe floating diffusion layer 312, the photodiode 316 is initialized inparallel with the initialization of the floating diffusion layer 312.

The solid-state image sensor 200 starts AD conversion of the P-phaselevel (reset level) (step S905). Then, the solid-state image sensor 200determines whether or not the trigger signal XTRIG is input during ADconversion of the P-phase level (step S906).

If the trigger signal XTRIG is input during AD conversion of the P-phaselevel (step S906: Yes), the solid-state image sensor 200 initializes thephotodiode 316 (step S907), and repeats step S905 and subsequent steps.

On the other hand, if the trigger signal XTRIG is not input during theAD conversion of the P-phase level (step S906: No), the solid-stateimage sensor 200 transfers electric charges to the floating diffusionlayer 312 (step S908) and starts AD conversion of the D-phase level(signal level) (step S909). Note that, if the trigger signal XTRIG isinput during the transfer of electric charges, the photodiode 316 isinitialized in parallel with the transfer of electric charges.

Then, the solid-state image sensor 200 determines whether or not thetrigger signal XTRIG is input during the AD conversion of the D-phaselevel (step S910).

If the trigger signal XTRIG is input during AD conversion of the D-phaselevel (step S910: Yes), the solid-state image sensor 200 initializes thephotodiode 316 (step S911), and repeats step S909 and subsequent steps.

On the other hand, if the trigger signal XTRIG is not input during ADconversion of the D-phase level (step S910: No), the solid-state imagesensor 200 determines whether or not the trigger signal XTRIG is inputafter the conversion of the D-phase level (step S912). If the triggersignal XTRIG is not input after the conversion of the D-phase level(step S912: No), the solid-state image sensor 200 repeats step S912.

On the other hand, if the trigger signal XTRIG is input after theconversion of the D-phase level (step S912: Yes), the solid-state imagesensor 200 repeatedly performs step S901 and subsequent steps.

As described above, according to the first embodiment of the presenttechnology, since the transfer transistor 315 transfers electric chargesfrom the photodiode 316 to the analog memory 314 when the exposureperiod ends, the exposure can be started before the transfer to thefloating diffusion layer 312.

First Modification

In the above-described first embodiment, pixel data is read from all thepixels. However, since there is no selection transistor provided in eachpixel, the first embodiment cannot support an application that readspixel data from some of the pixels. A solid-state image sensor 200 of afirst modification of the first embodiment is different from the firstembodiment in that a selection transistor is added.

FIG. 15 is a circuit diagram showing a configuration example of a pixelcircuit 310, a differential input circuit 330, a voltage conversioncircuit 340, and a positive feedback circuit 350 of the firstmodification of the first embodiment of the present technology. Thepixel circuit 310 of the first modification of the first embodiment isdifferent from the first embodiment in that it further includes a sourcefollower transistor 371, a selection transistor 372, and a cascodetransistor 373. For example, N-type MOS transistors are used as thesetransistors.

The source follower transistor 371 is included in a source followercircuit. For example, the gate of the source follower transistor 371 isconnected to a floating diffusion layer 312, the drain of the sourcefollower transistor 371 is connected to a power supply terminal, and thesource of the source follower transistor 371 is connected to the drainof the selection transistor 372.

The selection transistor 372 outputs a signal from the source of thesource follower transistor 371 to the differential input circuit 330 asa pixel signal SIG, according to a selection signal X from the pixeldriving circuit 250.

The cascode transistor 373 is a transistor cascode-connected to theselection transistor 372. A drive signal CS from the pixel drivingcircuit 250 is input to the gate of the cascode transistor 373. Thedrive signal CS can control the amplification factor of the pixelcircuit 310.

Note that while a light receiving chip 201 and a circuit chip 202 areseparated in the differential input circuit 330 in the firstmodification of the first embodiment, too, the separating part is notlimited to this configuration. For example, the light receiving chip 201and the circuit chip 202 can be separated at a connection point betweenthe pixel circuit 310 and the differential input circuit 330.

As described above, according to the first modification of the firstembodiment of the present technology, since the selection transistor 372that outputs the pixel signal SIG according to the selection signal isadded, it is possible to selectively read the pixel data of some of thepixels.

Second Modification

In the above-described first embodiment, when the trigger signal XTRIGis input during AD conversion of the P-phase level or the D-level, theAD conversion is redone to remove offset due to initialization of thephotodiode 316 (i.e., start of exposure). However, the read time becomeslonger because of the additional AD conversion. A second modification ofthe first embodiment is different from the first embodiment in that,when a trigger signal XTRIG is input during AD conversion, exposure isstarted after waiting until the end of the AD conversion, so that theneed for additional AD conversion is eliminated.

FIG. 16 is an example of a state transition diagram of the secondmodification of the first embodiment of the present technology. When thetrigger signal XTRIG is input in either a state 620 duringinitialization of a floating diffusion layer 312 or a state 650 duringAD conversion of the P-phase level, a solid-state image sensor 200 doesnot start exposure at that point, and does not perform additional ADconversion. Additionally, when the trigger signal XTRIG is input ineither a state 660 during transfer of electric charges or a state 640during AD conversion of the D-phase level, the solid-state image sensor200 similarly does not start exposure at that point, and does notperform additional AD conversion. Then, in these cases, the solid-stateimage sensor 200 starts exposure when the conversion of the D-phaselevel is completed.

FIG. 17 is a timing chart of the second modification of the firstembodiment of the present technology. In FIG. 17, the control up totiming T16 when the transfer of electric charges to the floatingdiffusion layer 312 ends is similar to that in FIG. 9.

When the trigger signal XTRIG is input at timing T17 during ADconversion of the D-phase level (signal level), the solid-state imagesensor 200 temporarily holds a flag indicating that the trigger signalXTRIG has been input in its internal register or the like. Additionally,the AD conversion is not redone. Then, at timing T18 when the ADconversion of the D-phase level ends, on the basis of the flag, thepixel driving circuit 250 supplies a high-level drive signal OFG untiltiming T19 when a pulse period elapses. As a result, the photodiode 316is initialized.

As described above, according to the second modification of the firstembodiment of the present technology, when the trigger signal XTRIG isinput during AD conversion, the solid-state image sensor 200 waits untilthe end of the AD conversion before starting the next exposure. Thiseliminates the need for additional AD conversion, and thus the read timecan be made shorter than the first embodiment in which additional ADconversion is performed.

Third Modification

In the above-described first embodiment, when the trigger signal XTRIGis input during AD conversion of the P-phase level or the D-phase level,the AD conversion is redone to remove offset due to initialization ofthe photodiode 316 (i.e., start of exposure). However, in a case wheredark current correction is performed, the dark current correctionsufficiently removes offset. Hence, the need for redoing AD conversionis eliminated. A third modification of the first embodiment is differentfrom the first embodiment in that exposure is started without performingadditional AD conversion, and offset is removed by dark currentcorrection.

FIG. 18 is an example of a plan view of a pixel array unit 240 of thethird modification of the first embodiment of the present technology.The pixel array unit 240 of the third modification of the firstembodiment is different from the first embodiment in that multiplelight-shielded pixels 301 and multiple effective pixels 302 are arrangedin a two-dimensional lattice shape.

The light-shielded pixel 301 is a pixel shielded from light, and theeffective pixel 302 is a pixel not shielded from light. Theconfigurations of the light-shielded pixel 301 and the effective pixel302 are the similar to that of the pixel 300 of the first embodiment.

Additionally, the light-shielded pixels 301 are arranged in a differentrow from the effective pixels 302, for example. Note that thelight-shielded pixels 301 may further be arranged in a different columnfrom the effective pixels 302.

FIG. 19 is an example of a state transition diagram of the thirdmodification of the first embodiment of the present technology.

When a trigger signal XTRIG is input in either a state 620 duringinitialization of a floating diffusion layer 312 or a state 650 duringAD conversion of the P-phase level, a solid-state image sensor 200starts exposure at that point, and does not perform additional ADconversion. Additionally, when the trigger signal XTRIG is input ineither a state 660 during transfer of electric charges or a state 640during AD conversion of the D-phase level, the solid-state image sensor200 similarly starts exposure at that point, and does not performadditional AD conversion.

FIG. 20 is a timing chart of the third modification of the firstembodiment of the present technology. The control up to timing T16 whenthe transfer of electric charges to the floating diffusion layer 312ends is similar to that in FIG. 9.

When the trigger signal XTRIG is input at timing T17 during ADconversion of the D-phase level (signal level), the pixel drivingcircuit 250 supplies a high-level drive signal OFG until timing T18 whena pulse period elapses. As a result, the photodiode 316 is initialized.On the other hand, AD conversion of the D-phase level is continuouslyperformed in parallel with the initialization of the photodiode 316.

Additionally, after the D-phase conversion, a signal processing unit 270obtains the dark current from light-shielded pixel data of thelight-shielded pixel 301, and performs dark current correction forremoving the dark current from effective pixel data of the effectivepixel 302. As a result, offset is removed. This eliminates the need foradditional AD conversion for offset removal.

As described above, according to the third modification of the firstembodiment of the present technology, since the signal processing unit270 performs dark current correction for removing dark current fromeffective pixel data of the effective pixel 302, the need for additionalAD conversion for offset removal is eliminated. As a result, the readtime can be made shorter than the first embodiment in which additionalAD conversion is performed.

2. Second Embodiment

While the ADC 320 is arranged for each pixel in the above-describedfirst embodiment, the number of ADCs 320 increases as the number ofpixels increases, which may increase the cost and the circuit scale. Asolid-state image sensor 200 of a second embodiment is different fromthe first embodiment in that multiple pixels 300 share one ADC 320.

FIG. 21 is an example of a plan view of a pixel array unit 240 of thesecond embodiment of the present technology. The pixel array unit 240 ofthe second embodiment is different from the first embodiment in thatmultiple pixel blocks 400 are arranged in a two-dimensional latticeshape.

FIG. 22 is a block diagram showing a configuration example of the pixelblock 400 of the second embodiment of the present technology. In thepixel block 400, multiple pixel circuits such as pixel circuits 411,412, and 413 and one ADC 320 are arranged. For example, eight pixelcircuits of two rows×four columns and four pixel circuits of tworows×two columns are arranged in the pixel block 400.

The circuit configurations of the pixel circuits 411, 412, and 413 aresimilar to that of the pixel circuit 310 of the first embodiment. TheADC 320 is shared by these pixel circuits.

The pixel driving circuit 250 supplies a drive signal OFGn (n is aninteger), a transfer signal TRGn, a reset signal RSTn, and a transfersignal TRXn to the nth pixel circuit to drive the pixel circuit.Additionally, when a trigger signal XTRIG is input, the pixel drivingcircuit 250 selects and drives any one of the multiple pixel circuitsfor each pixel block 400. As a result, one piece of pixel data is readfor each pixel block 400, and image data is generated. For this reason,the resolution of the image data of the second embodiment is lower thanthat of the first embodiment in which all pixels are read.

FIG. 23 is a timing chart showing an example of the operation of animaging device of the second embodiment of the present technology. Inthe first embodiment, when the trigger signal XTRIG is input during anexposure period, the next exposure cannot be started until the currentexposure period ends. On the other hand, in the second embodiment, evenif the trigger signal XTRIG is input during an exposure period, thesolid-state image sensor 200 can start the next exposure.

For example, when the trigger signal XTRIG is input at timing T53, thepixel driving circuit 250 drives the pixel circuit 411 in the pixelblock 400 to start exposure. Then, when the trigger signal XTRIG isinput at timing T54 before the exposure period of the pixel circuit 411ends, the pixel driving circuit 250 drives the pixel circuit 412 in thepixel block 400 to start exposure. Then, at timing T55 when the exposureperiod of the pixel circuit 411 ends, the ADC 320 starts AD conversionof the pixel signal corresponding to the pixel circuit 411. Then, attiming T56 when the exposure period of the pixel circuit 412 ends, theADC 320 starts AD conversion of the pixel signal corresponding to thepixel circuit 412.

Additionally, when the trigger signal XTRIG is input at timing T57, thepixel driving circuit 250 drives the pixel circuit 411 in the pixelblock 400 to start exposure. Then, when the trigger signal XTRIG isinput oat timing T58 before the exposure period of the pixel circuit 411ends, the pixel driving circuit 250 drives the pixel circuit 412 in thepixel block 400 to start exposure. Then, when the trigger signal XTRIGis input at timing T69 when the exposure period of the pixel circuit 411ends, the pixel driving circuit 250 drives the pixel circuit 413 in thepixel block 400 to start exposure. Additionally, at timing T59 when theexposure period of the pixel circuit 411 ends, the ADC 320 starts ADconversion of the pixel signal corresponding to the pixel circuit 411.Then, at timing T60 when the exposure period of the pixel circuit 412ends, the ADC 320 starts AD conversion of the pixel signal correspondingto the pixel circuit 412. Additionally, at timing T61 when the exposureperiod of the pixel circuit 413 ends, the ADC 320 starts AD conversionof the pixel signal corresponding to the pixel circuit 413.

As described above, even if the trigger signal XTRIG is input during theexposure of the pixel circuit 411, the solid-state image sensor 200 candrive the pixel circuit 412 or the pixel circuit 413 and start the nextexposure. Note, however, that since AD conversion can only be performedfor one pixel at a time, if the interval of the trigger signal XTRIG isshorter than the time required for AD conversion, the solid-state imagesensor 200 cannot start exposure. In this case, the solid-state imagesensor 200 only needs to start exposure after the elapse of the timerequired for AD conversion from the timing of the most recent triggersignal XTRIG, for example. Additionally, the solid-state image sensor200 is similarly unable to start the next exposure when the triggersignal XTRIG is input during exposure of all the pixel circuits in thepixel block 400. In this case, the solid-state image sensor 200 onlyneeds to start the next exposure when the exposure period of one of thepixel circuits ends, for example.

Note that the first, second, or third modification is applicable to thesecond embodiment as in the case of the first embodiment.

As described above, according to the second embodiment of the presenttechnology, since multiple pixels share one ADC 320, the number of ADCs320 per pixel can be reduced compared to the case where the ADC 320 isarranged for each pixel. As a result, the circuit scale and cost of thesolid-state image sensor 200 can be reduced.

3. Third Embodiment

In the above-described first embodiment, one analog memory 314 isarranged for each pixel. However, with this configuration, when anexposure period shorter than the AD conversion period is set, ifmultiple trigger signals XTRIG are input within the AD conversionperiod, image data cannot be captured in response to each triggersignal. A solid-state image sensor 200 of a third embodiment isdifferent from the first embodiment in that multiple analog memories arearranged for each pixel to capture multiple pieces of image data.

FIG. 24 is a circuit diagram showing a configuration example of a pixelcircuit 310 of the third embodiment of the present technology. The pixelcircuit 310 of the third embodiment includes a set transistor 311, afloating diffusion layer 312, multiple memory circuits such as memorycircuits 421 and 422, a photodiode 316, and a discharge transistor 317.The multiple memory circuits are commonly connected to and share thefloating diffusion layer 312 and the photodiode 316. Circuits at thesubsequent stage of the pixel circuit 310 are similar to those of thefirst embodiment.

The memory circuit 421 includes transfer transistors 313 and 315 and ananalog memory 314. The circuit configuration of the memory circuit 422is similar to that of the memory circuit 421.

A pixel driving circuit 250 supplies a transfer signal TRGn and atransfer signal TRXn to the n-th memory circuit to transfer electriccharges. Additionally, when a trigger signal XTRIG is input, the pixeldriving circuit 250 selects, for each pixel circuit 310, any one of themultiple memory circuits, and transfers the electric charges. As aresult, when an exposure period shorter than the AD conversion period isset, if multiple trigger signals XTRIG are input within the ADconversion period, the electric charges in the photodiode 316 can besequentially transferred to the multiple memory circuits. Accordingly,it is possible to sequentially generate multiple pieces of image datahaving exposure periods shorter than the AD conversion period.

Note that the first, second, or third modification is applicable to thethird embodiment as in the case of the first embodiment.

As described above, according to the third embodiment of the presenttechnology, since the pixel driving circuit 250 sequentially transferselectric charges to the multiple memory circuits, multiple pieces ofimage data can be sequentially captured in exposure periods shorter thanthe AD conversion period.

<4. Example of Application to Movable Body>

The technology of the present disclosure (present technology) can beapplied to various products. For example, the technology of the presentdisclosure may be implemented as a device mounted on any type of movablebodies including a car, an electric car, a hybrid electric car, amotorcycle, a bicycle, a personal mobility, an airplane, a drone, aship, a robot, and the like.

FIG. 25 is a block diagram showing a schematic configuration example ofa vehicle control system which is an example of a mobile control systemto which the technology of the present disclosure can be applied.

A vehicle control system 12000 includes multiple electronic controlunits connected through a communication network 12001. In the exampleshown in FIG. 25, the vehicle control system 12000 includes a drivesystem control unit 12010, a body system control unit 12020, an outsideinformation detection unit 12030, an inside information detection unit12040, and an integrated control unit 12050. Additionally, as afunctional configuration of the integrated control unit 12050, amicrocomputer 12051, an audio image output unit 12052, and an in-carnetwork interface (I/F) 12053 are shown.

The drive system control unit 12010 controls the operation of devicesrelated to the drive system of the vehicle according to variousprograms. For example, the drive system control unit 12010 functions asa controller of a drive force generation device for generating a driveforce of a vehicle such as an internal combustion engine or a drivemotor, a drive force transmission mechanism for transmitting the driveforce to wheels, a steering mechanism that adjusts the steering angle ofthe vehicle, a braking device that generates a braking force of thevehicle, and the like.

The body system control unit 12020 controls the operation of variousdevices equipped on the vehicle body according to various programs. Forexample, the body system control unit 12020 functions as a controller ofa keyless entry system, a smart key system, a power window device, orvarious lamps such as a headlamp, a back lamp, a brake lamp, a blinker,or a fog lamp. In this case, the body system control unit 12020 mayreceive input of radio waves transmitted from a portable devicesubstituting a key or signals of various switches. The body systemcontrol unit 12020 receives input of these radio waves or signals, andcontrols a door lock device, a power window device, a lamp, and the likeof the vehicle.

The outside information detection unit 12030 detects information outsidethe vehicle equipped with the vehicle control system 12000. For example,an imaging unit 12031 is connected to the outside information detectionunit 12030. The outside information detection unit 12030 causes theimaging unit 12031 to capture an image of the outside of the vehicle,and receives the captured image. The outside information detection unit12030 may perform object detection processing or distance detectionprocessing of a person, a vehicle, an obstacle, a sign, characters on aroad surface, or the like on the basis of the received image.

The imaging unit 12031 is an optical sensor that receives light andoutputs an electrical signal corresponding to the amount of lightreceived. The imaging unit 12031 can output an electric signal as animage or can output the electrical signal as distance measurementinformation. Additionally, the light received by the imaging unit 12031may be visible light or non-visible light such as infrared light.

The inside information detection unit 12040 detects information insidethe vehicle. For example, a driver state detection unit 12041 thatdetects a state of a driver is connected to the inside informationdetection unit 12040. The driver state detection unit 12041 includes acamera for capturing an image of the driver, for example, and the insideinformation detection unit 12040 may calculate the degree of fatigue orconcentration of the driver or determine whether or not the driver isasleep, on the basis of the detection information input from the driverstate detection unit 12041.

The microcomputer 12051 can calculate a control target value of thedrive force generation device, the steering mechanism, or the brakingdevice on the basis of the information outside or inside the vehicleacquired by the outside information detection unit 12030 or the insideinformation detection unit 12040, and output a control command to thedrive system control unit 12010. For example, the microcomputer 12051can perform coordinated control aimed to achieve functions of anadvanced driver assistance system (ADAS) including collision avoidanceor shock mitigation of a vehicle, follow-up traveling based on aninter-vehicle distance, vehicle speed maintenance traveling, vehiclecollision warning, vehicle lane departure warning, or the like.

Additionally, the microcomputer 12051 can control the drive forcegeneration device, the steering mechanism, the braking device, or thelike on the basis of the information around the vehicle acquired by theoutside information detection unit 12030 or the inside informationdetection unit 12040, to perform coordinated control aimed for automaticdriving of traveling autonomously without depending on the driver'soperation, for example.

Additionally, the microcomputer 12051 can output a control command tothe body system control unit 12020 on the basis of the informationoutside the vehicle acquired by the outside information detection unit12030. For example, the microcomputer 12051 can control the headlampaccording to the position of the preceding vehicle or oncoming vehicledetected by the outside information detection unit 12030, and performcoordinated control aimed for glare prevention such as switching fromhigh beam to low beam.

The audio image output unit 12052 transmits an output signal of at leastone of audio or an image to an output device capable of visually oraurally giving notification of information to a passenger or the outsideof a vehicle. In the example of FIG. 25, an audio speaker 12061, adisplay unit 12062, and an instrument panel 12063 are shown as examplesof the output device. The display unit 12062 may include at least one ofan onboard display or a head-up display, for example.

FIG. 26 is a diagram showing an example of the installation position ofthe imaging unit 12031.

In FIG. 26, imaging units 12101, 12102, 12103, 12104, and 12105 areincluded as the imaging unit 12031.

For example, the imaging units 12101, 12102, 12103, 12104, and 12105 areprovided in positions such as a front nose, a side mirror, a rearbumper, a back door, and an upper portion of a windshield in the vehicleinterior of the vehicle 12100. The imaging unit 12101 provided on thefront nose and the imaging unit 12105 provided on the upper portion ofthe windshield in the vehicle interior mainly acquire images of thefront of the vehicle 12100. The imaging units 12102 and 12103 providedon the side mirrors mainly acquire images of the sides of the vehicle12100. The imaging unit 12104 provided on the rear bumper or the backdoor mainly acquires an image of the rear of the vehicle 12100. Theimaging unit 12105 provided on the upper portion of the windshield inthe vehicle interior is mainly used to detect a preceding vehicle or apedestrian, an obstacle, a traffic light, a traffic sign, a lane, or thelike.

Note that FIG. 26 shows an example of the imaging ranges of the imagingunits 12101 to 12104. An imaging range 12111 indicates the imaging rangeof the imaging unit 12101 provided on the front nose, imaging ranges12112 and 12113 indicate the imaging ranges of the imaging units 12102and 12103 provided on the side mirrors, respectively, and an imagingrange 12114 indicates the imaging range of the imaging unit 12104provided on the rear bumper or the back door. For example, bysuperimposing the pieces of image data captured by the imaging units12101 to 12104, a bird's eye view image of the vehicle 12100 as viewedfrom above can be obtained.

At least one of the imaging units 12101 to 12104 may have a function ofacquiring distance information. For example, at least one of the imagingunits 12101 to 12104 may be a stereo camera including multiple imagingdevices, or may be an imaging device having pixels for phase differencedetection.

For example, the microcomputer 12051 can measure the distance to eachthree-dimensional object in the imaging ranges 12111 to 12114 and thetemporal change of this distance (relative velocity with respect tovehicle 12100) on the basis of the distance information obtained fromthe imaging units 12101 to 12104, to extract, as a preceding vehicle,the closest three-dimensional object on the traveling path of thevehicle 12100 in particular, the three-dimensional object traveling at apredetermined speed (e.g., 0 km/h or more) in substantially the samedirection as the vehicle 12100. Moreover, the microcomputer 12051 canset an inter-vehicle distance to be secured in advance before thepreceding vehicle, and perform automatic brake control (includingfollow-up stop control), automatic acceleration control (includingfollow-up start control), and the like. As described above, it ispossible to perform coordinated control aimed for automatic driving oftraveling autonomously without depending on the driver's operation, forexample.

For example, on the basis of the distance information obtained from theimaging units 12101 to 12104, the microcomputer 12051 can extractthree-dimensional object data regarding three-dimensional objects byclassifying the data into a two-wheeled vehicle, an ordinary vehicle, alarge vehicle, a pedestrian, and other three-dimensional objects such asa telephone pole, and use the data for automatic avoidance of obstacles.For example, the microcomputer 12051 identifies obstacles around thevehicle 12100 as obstacles visible or hardly visible to the driver ofthe vehicle 12100. Then, the microcomputer 12051 can determine thecollision risk indicating the degree of risk of collision with eachobstacle, and when the collision risk is a setting value or more andthere is a possibility of a collision, the microcomputer 12051 canperform driving support for collision avoidance by outputting a warningto the driver through the audio speaker 12061 or the display unit 12062,or by performing forcible deceleration or avoidance steering through thedrive system control unit 12010.

At least one of the imaging units 12101 to 12104 may be an infraredcamera that detects infrared light.

For example, the microcomputer 12051 can recognize a pedestrian bydetermining whether or not a pedestrian is present in the imagescaptured by the imaging units 12101 to 12104. Such pedestrianrecognition is performed by a procedure of extracting feature points inimages captured by the imaging units 12101 to 12104 as infrared cameras,and a procedure of performing pattern matching processing on a series offeature points indicating the outline of an object to determine whetheror not the object is a pedestrian, for example. When the microcomputer12051 determines that a pedestrian is present in the images captured bythe imaging units 12101 to 12104 and recognizes the pedestrian, theaudio image output unit 12052 controls the display unit 12062, so that asquare outline for emphasis is superimposed on the recognizedpedestrian. Additionally, the audio image output unit 12052 may controlthe display unit 12062, so that an icon or the like indicating apedestrian is displayed in a desired position.

Hereinabove, an example of the vehicle control system to which thetechnology of the present disclosure can be applied has been described.Of the above-described configuration, the technology according to thepresent disclosure is applicable to the imaging unit 12031, for example.Specifically, the imaging device 100 of FIG. 1 can be applied to theimaging unit 12031, for example. By applying the technology according tothe present disclosure to the imaging unit 12031, the dead period can beshortened, and thus the convenience and reliability of the system can beimproved.

Note that the above-described embodiments are an example for embodyingthe present technology, and the matters in the embodiments and thematters specifying the invention in the claims have a correspondingrelationship. Similarly, the matters specifying the invention in theclaims and the matters having the same names in the embodiments of thepresent technology have a correspondence relationship. Note, however,that the present technology is not limited to the embodiments, and canbe embodied by variously modifying the embodiments without departingfrom the gist of the present technology.

Note that the present technology can also be configured in the followingmanner.

(1) A solid-state image sensor including:

a photodiode that generates electric charges by photoelectricconversion;

an electric charge accumulation unit that accumulates the electriccharges;

a floating diffusion layer that converts the electric charges into asignal level corresponding to the amount of the electric charges;

an exposure end transfer transistor that transfers the electric chargesfrom the photodiode to the electric charge accumulation unit when apredetermined exposure period ends;

a reset transistor that initializes a voltage of the floating diffusionlayer to a predetermined reset level when the exposure period ends;

a discharge transistor that, when a new exposure period is started afterthe electric charges are transferred to the electric charge accumulationunit, discharges electric charges newly generated in the photodiode; and

a conversion end transfer transistor that, when processing of convertinga predetermined reset level into a digital signal ends, transfers theelectric charges from the electric charge accumulation unit to thefloating diffusion layer.

(2) The solid-state image sensor according to (1) above, furtherincluding an analog-to-digital converter that sequentially performsreset level conversion processing of converting the reset level into thedigital signal, and signal level conversion processing of sequentiallyconverting the signal level into a digital signal.

(3) The solid-state image sensor according to (2) above, in which

the photodiode, the electric charge accumulation unit, the floatingdiffusion layer, the exposure end transfer transistor, the dischargereset transistor, the conversion end transfer transistor, and the resettransistor are arranged on a predetermined light receiving board, and

at least a part of the analog-to-digital converter is arranged on apredetermined circuit board stacked on the predetermined light receivingboard.

(4) The solid-state image sensor according to any one of (1) to (3)above, further including:

a source follower transistor that has a gate connected to the floatingdiffusion layer and a drain connected to a power supply terminal;

a selection transistor that outputs a signal from a source of the sourcefollower transistor to the analog-to-digital converter according to apredetermined selection signal; and

a cascode transistor that is cascode-connected to the selectiontransistor.

(5) The solid-state image sensor according to any one of (1) to (4)above, in which

the photodiode, the electric charge accumulation unit, the floatingdiffusion layer, the exposure end transfer transistor, the photodiodereset transistor, the conversion end transfer transistor, and thefloating diffusion layer reset transistor are arranged in each ofmultiple pixels.

(6) The solid-state image sensor according to (5) above, in which

the electric charge accumulation unit, the exposure end transfertransistor, and the conversion end transfer transistor are arranged ineach of multiple memory circuits sharing the photodiode and the floatingdiffusion layer.

(7) The solid-state image sensor according to (5) above, in which

the analog-to-digital converter is arranged in each of the multiplepixels.

(8) The solid-state image sensor according to (5) above, in which

the analog-to-digital converter is arranged in each of multiple pixelblocks each including a predetermined number of pixels.

(9) The solid-state image sensor according to any one of (1) to (8)above, in which

the analog-to-digital converter repeats the reset level conversionprocessing from the beginning in a case where the amount of the electriccharges in the photodiode is initialized during the reset levelconversion processing.

(10) The solid-state image sensor according to any one of (1) to (9)above, in which

the analog-to-digital converter repeats the signal level conversionprocessing from the beginning in a case where the amount of the electriccharges in the photodiode is initialized during the signal levelconversion processing.

(11) The solid-state image sensor according to any one of (1) to (10)above, further including

a signal processing unit that performs correlated double samplingprocessing for obtaining, as image data, a difference between thedigital signal obtained by converting the reset level and the digitalsignal obtained by converting the signal level.

(12) The solid-state image sensor according to (11) above, in which

the signal processing unit further performs dark current correction forremoving dark current from the image data.

(13) An imaging device including:

a photodiode that generates electric charges by photoelectricconversion;

an electric charge accumulation unit that accumulates the electriccharges;

a floating diffusion layer that converts the electric charges into asignal level corresponding to the amount of the electric charges;

an exposure end transfer transistor that transfers the electric chargesfrom the photodiode to the electric charge accumulation unit when apredetermined exposure period ends;

a reset transistor that initializes a voltage of the floating diffusionlayer to a predetermined reset level when the exposure period ends;

a discharge transistor that, when a new exposure period is started afterthe electric charges are transferred to the electric charge accumulationunit, discharges electric charges newly generated in the photodiode;

a conversion end transfer transistor that, when processing of convertinga predetermined reset level into a digital signal ends, transfers theelectric charges from the electric charge accumulation unit to thefloating diffusion layer; and

a signal processing unit that processes the digital signal obtained byconverting the reset level and a digital signal obtained by convertingthe signal level.

(14) A method of controlling a solid-state image sensor, including:

an exposure end transfer procedure of transferring electric charges froma photodiode that generates electric charges by photoelectric conversionwhen a predetermined exposure period ends to an electric chargeaccumulation unit that accumulates the electric charges;

a reset procedure of initializing a voltage of the floating diffusionlayer to a predetermined reset level when the exposure period ends;

a discharge procedure of, when a new exposure period is started afterthe electric charges are transferred to the electric charge accumulationunit, discharging electric charges newly generated in the photodiode;and

a conversion end transfer procedure of, when processing of converting apredetermined reset level into a digital signal ends, transferring theelectric charges from the electric charge accumulation unit to thefloating diffusion layer that converts the electric charges into asignal level corresponding to the amount of the electric charges.

REFERENCE SIGNS LIST

100 Imaging device110 Optical unit120 DSP circuit130 Display unit140 Operation unit

150 Bus

160 Frame memory170 Storage unit180 Power supply unit200 Solid-state image sensor201 Light receiving chip202 Circuit chip

210 DAC

220 Time code generation unit230 Vertical driving circuit240 Pixel array unit241 Time code transfer section250 Pixel driving circuit260 Timing generation circuit270 Signal processing unit

300 Pixel

301 Light-shielded pixel302 Effective pixel310, 411, 412, 413 Pixel circuit311 Reset transistor312 Floating diffusion layer313, 315 Transfer transistor314 Analog memory

316 Photodiode

317 Discharge transistor

320 ADC

321 Comparator circuit330 Differential input circuit331, 334, 336, 351, 352, 355, 356 PMOS transistor332, 333, 335, 341, 353, 354, 357 NMOS transistor340 Voltage conversion circuit350 Positive feedback circuit360 Data storage section371 Source follower transistor372 Selection transistor373 Cascode transistor400 Pixel block421, 422 Memory circuit510 Belt conveyor

511 Product

520 Detection sensor

1. A solid-state image sensor comprising: a photodiode that generateselectric charges by photoelectric conversion; an electric chargeaccumulation unit that accumulates the electric charges; a floatingdiffusion layer that converts the electric charges into a signal levelcorresponding to the amount of the electric charges; an exposure endtransfer transistor that transfers the electric charges from thephotodiode to the electric charge accumulation unit when a predeterminedexposure period ends; a reset transistor that initializes a voltage ofthe floating diffusion layer to a predetermined reset level when theexposure period ends; a discharge transistor that, when a new exposureperiod is started after the electric charges are transferred to theelectric charge accumulation unit, discharges electric charges newlygenerated in the photodiode; and a conversion end transfer transistorthat, when processing of converting the predetermined reset level into adigital signal ends, transfers the electric charges from the electriccharge accumulation unit to the floating diffusion layer.
 2. Thesolid-state image sensor according to claim 1, further comprising ananalog-to-digital converter that sequentially performs reset levelconversion processing of converting the reset level into the digitalsignal, and signal level conversion processing of sequentiallyconverting the signal level into a digital signal.
 3. The solid-stateimage sensor according to claim 2 wherein the photodiode, the electriccharge accumulation unit, the floating diffusion layer, the exposure endtransfer transistor, the discharge transistor, the conversion endtransfer transistor, and the reset transistor are arranged on apredetermined light receiving board, and at least a part of theanalog-to-digital converter is arranged on a predetermined circuit boardstacked on the predetermined light receiving board.
 4. The solid-stateimage sensor according to claim 1, further comprising: a source followertransistor that has a gate connected to the floating diffusion layer anda drain connected to a power supply terminal; a selection transistorthat outputs a signal from a source of the source follower transistor tothe analog-to-digital converter according to a predetermined selectionsignal; and a cascode transistor that is cascode-connected to theselection transistor.
 5. The solid-state image sensor according to claim1, wherein the photodiode, the electric charge accumulation unit, thefloating diffusion layer, the exposure end transfer transistor, thephotodiode reset transistor, the conversion end transfer transistor, andthe floating diffusion layer reset transistor are arranged in each of aplurality of pixels.
 6. The solid-state image sensor according to claim5, wherein the electric charge accumulation unit, the exposure endtransfer transistor, and the conversion end transfer transistor arearranged in each of a plurality of memory circuits sharing thephotodiode and the floating diffusion layer.
 7. The solid-state imagesensor according to claim 5, wherein the analog-to-digital converter isarranged in each of the plurality of pixels.
 8. The solid-state imagesensor according to claim 5, wherein the analog-to-digital converter isarranged in each of a plurality of pixel blocks each including apredetermined number of pixels.
 9. The solid-state image sensoraccording to claim 1, wherein the analog-to-digital converter repeatsthe reset level conversion processing from the beginning in a case wherethe amount of the electric charges in the photodiode is initializedduring the reset level conversion processing.
 10. The solid-state imagesensor according to claim 1, wherein the analog-to-digital converterrepeats the signal level conversion processing from the beginning in acase where the amount of the electric charges in the photodiode isinitialized during the signal level conversion processing.
 11. Thesolid-state image sensor according to claim 1, further comprising asignal processing unit that performs correlated double samplingprocessing for obtaining, as image data, a difference between thedigital signal obtained by converting the reset level and the digitalsignal obtained by converting the signal level.
 12. The solid-stateimage sensor according to claim 11, wherein the signal processing unitfurther performs dark current correction for removing dark current fromthe image data.
 13. An imaging device comprising: a photodiode thatgenerates electric charges by photoelectric conversion; an electriccharge accumulation unit that accumulates the electric charges; afloating diffusion layer that converts the electric charges into asignal level corresponding to the amount of the electric charges; anexposure end transfer transistor that transfers the electric chargesfrom the photodiode to the electric charge accumulation unit when apredetermined exposure period ends; a reset transistor that initializesa voltage of the floating diffusion layer to a predetermined reset levelwhen the exposure period ends; a discharge transistor that, when a newexposure period is started after the electric charges are transferred tothe electric charge accumulation unit, discharges electric charges newlygenerated in the photodiode; a conversion end transfer transistor that,when processing of converting a predetermined reset level into a digitalsignal ends, transfers the electric charges from the electric chargeaccumulation unit to the floating diffusion layer; and a signalprocessing unit that processes the digital signal obtained by convertingthe reset level and a digital signal obtained by converting the signallevel.
 14. A method of controlling a solid-state image sensor,comprising: an exposure end transfer procedure of transferring electriccharges from a photodiode that generates electric charges byphotoelectric conversion when a predetermined exposure period ends to anelectric charge accumulation unit that accumulates the electric charges;a reset procedure of initializing a voltage of the floating diffusionlayer to a predetermined reset level when the exposure period ends; adischarge procedure of, when a new exposure period is started after theelectric charges are transferred to the electric charge accumulationunit, discharging electric charges newly generated in the photodiode;and a conversion end transfer procedure of, when processing ofconverting a predetermined reset level into a digital signal ends,transferring the electric charges from the electric charge accumulationunit to the floating diffusion layer that converts the electric chargesinto a signal level corresponding to the amount of the electric charges.